Finally remove UCIInputParser class altogether

Finally remove UCIInputParser class altogether

Class UCIInputParser is now a typedef of a std::istringstream,
this greatly simplifies the code, especially the many conversions
from string to integer are now handled automatically by the
stream instead of relying on a chunk of C-style atoi() calls.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>